It may be argued that psychological relativity contributes substantially to the variance in human behavior. That is, the response to day to day events such as the work environment, salary, interpersonal interactions, etc., is influenced not only by the characteristics of these events themselves, but also by an individual's expectancies. Thus, of two individuals exposed to the same event, one could be disappointed and the other elated because of differential expectancies that they brought to the situation. Disappointment may have physiological as well as psychological effects and major or repeated disappointment may lead to psychological or physical disorder. One form of relativity, incentive relativity, may be readily studied in animals and, in fact, a substantial amount is known about the behavioral principles governing such relativity. This proposal is concerned with the further investigation of an incentive relativity procedure in which rats are shifted from preferred to less preferred sucrose solutions. Rats with prior experience with a 32% sucrose solution will consume less of a 4% solution than animals that have experienced only the 4% solution. We have previously shown that this contrast effect is reduced by anxiolytic drugs, under specific conditions, and eliminated by lesions of the corticomedial area of the amygdala. Some of the research proposed here is concerned with estimating the degree of stress imposed by such a reward shift by assaying corticosterone responses over time in animals that are exposed to a variety of different reward shifts under different experimental conditions (nine experiments). Other experiments are concerned with the involvement of exogenous and endogenous opiates in recovery from reward loss. These studies will involve injection of opiate agonists and antagonists, sometimes in combination with benzodiazepine tranquilizers (four experiments). Another set of experiments is concerned with the function of the corticomedial aspect of the amygdala in the occurrence of contrast. These experiments will involve focal infusion into the amygdala of substances that have been shown to have effects when administered systemically. A final set of experiments is concerned with further defining the time course of contrast following a downshift in reward. All these studies are concerned with the long term goal of understanding incentive relativity in all of its psychological and physiological ramifications.